tube amplifier auto bias- accurate?

Eldartford, one cannot add on a slide rule, only multiple and divide and other operations, but no adding (nor subtracting, obviously). The scales are logarithmic to permit multiplication by adding powers. I still have my sliderule in my desk, for nostalgia!

Bob P.

"I wonder if Macs were the first ones to implement autobias successful in their vintage gears like the MC240s."

Doubtful. bias as a concept is as old as tubes, e.g. early part of the 1900s, 1910-1920 is when most basic concepts and methodologies were developed. Not much has changed since then. Things rediscovered, e.g. Parafeed, etc.

-Ed

Bob P. as the saying goes, "If you can't dazzle them with brains, baffle them with bull$#!^"

Ed your wrong on this one.
Only way you can bias a tube amp correctly is to use a scope and a dummy load. A440 cycles when it starts to clip you then adjust so the cross over notch disappears. You have to look at the wave form! If a manufacturer says its autobias its either full class A or if its not class A they are lying to you.

Bin...Actually it was Ed_sawyer who suggested that a voltage measurement was all that is required, and I merely pointed out that you can utilize a scope as a voltmeter. It doesn't make sense to do that, (like adding on the log scale of your sliderule) but it can be done. Most bias setting is done using a voltmeter, often a meter that is built into the amp.

Your method sounds good, although it's not obvious that the end result would be any different from using a voltmeter.